Biology subjects

Shanker, K.

Publications and source records attributed to Shanker, K..

12 recordsLinked to original sources

bioRxiv2026

Plumage colour structures global patterns of mixed-species bird flocks

Mixed-species groups (MSGs) pose a particular challenge for our understanding of sociality in animals. Though MSGs are widespread social assemblages that form to enhance foraging success and reduce predation risk of participants, the role of traits in mediating grouping has received less attention. In particular, the role of body colour has not been tested quantitatively, despite the fact that visual similarity can reduce individual predation risk. Here, we examine whether plumage colour structures mixed-species bird flocks (MSFs) at a global scale. Using data spanning four continents, we developed a new metric that quantifies colour similarity among flock participants and compared observed flocks to null assemblages constructed from all flocking species at each site. We further examined whether MSF participants represented a colour subset of the available colours in the regional species pool. We found striking evidence that birds in MSFs were more similar in colour than expected by chance across all sites, indicating that plumage colour is a non-random structuring trait that shapes assembly of flocks globally. The strength and prevalence of colour structuring varied across geographies, but not flock size. Within communities, MSF participants differed systematically in colour composition from the regional species pool, occupying a restricted region of colour space dominated by yellow and brown plumage. Thus, plumage colour affects MSFs influencing both overall flock participation as well as species co-occurrence within flocks. Our findings illustrate the importance of visual traits in structuring interspecific social systems, by highlighting that birds of a feather do indeed flock together.

ecology↗

bioRxiv2025

Out of sight, out of mind: Removal of predators by fisheries alters reef fish behaviour.

Pervasive human activities have led to the extirpation of predator species in many ecosystems. Understanding the extent and mechanisms by which such predator loss influences prey behaviour is critical for predicting the ecological consequences of trophic downgrading. We investigated reef fish behaviour in response to predator presence within and outside a protected area in the South Andaman Islands, India. We used 3D printed models to simulate the presence of two different types of predators; a sit-and-wait predator, a grouper (Mycteroperca rosacea) and a wide-ranging pursuit predator, a barracuda (Sphyraena barracuda). We recorded foraging, vigilance, and movement behaviours of herbivorous and invertivorous fish encountered in each plot. Overall, we found that fish were significantly more vigilant in response to both predator models compared to a non-predator control within protected areas but not outside protected areas. Foraging behaviour was suppressed by the predator treatments; however, herbivorous and invertivorous fish responded differently within protected areas. Fish movement behaviours also differed across predator treatments, prey foraging guilds, and areas. Anti-predator responses are thus highly contingent on habitat and both predator and prey traits. We highlight how the selective removal of predators by humans alters predation risk for prey and hence their risk-sensitive behaviours.

ecology↗

bioRxiv2025

Local extraction of predatory fish may initiate behaviourally mediated trophic cascades in coral reefs in the Andaman Islands.

Humans disproportionately target predators due to their higher economic and social value. This has led to widespread declines of predators in ecosystems worldwide leading to far-reaching effects on ecosystem processes. We investigate how the loss of predators from nearshore ecosystems due to fishing affects individual prey behaviour using a gradient of protection as a natural experiment. We collected data on piscivorous predator assemblages, reef habitats and prey behaviour within and outside two marine protected areas (MPAs) in the South Andaman Islands, India. As expected, predator abundance was significantly greater within MPAs. Similarly, we found greater coral cover and reduced algal cover within MPAs. In response, prey species, which included herbivorous and invertivorous fish, exhibited reduced movement and heightened vigilance inside MPAs. Additionally, prey individuals foraged at higher rates within MPAs. Habitat complexity and resource availability had complex effects on prey behaviours that varied across guilds. Our findings suggest that fishing directly alters the seascape of fear through the removal of predators. Fishing may also shape prey behaviour and ecological interactions indirectly through habitat degradation. Overall, this study highlights the need to study both direct and indirect consequences of human interactions with wild animals to understand their combined impacts on ecosystems.

ecology↗

bioRxiv2025

Human activities drive novel behaviours and transitions in dolphins

Intensifying human activities are reshaping coastal ecosystems, yet their impact on wildlife behaviour and survival remain poorly understood. We conducted drone-based focal-group follows of endangered Indian Ocean humpback dolphin groups in Goa, India, to quantify how tourism and fisheries jointly impact behavioural states and transitions. By integrating machine learning and georeferencing techniques, we found that both human activities triggered distinct behavioural transitions absent in undisturbed groups. Dolphins expressed escape behaviours exclusively near tourist boats and were more likely to transition into foraging near fishing nets (mostly purse-seines). Smaller groups reacted more strongly to tourist boats and interacted more frequently with fishing nets, especially in seasons when fish landing data showed a decline in their prey. These findings offer new insights into the behavioural mechanisms underlying the co-occurrence of coastal dolphins with humans and provide broader guidelines for managing tourism and fisheries to reduce anthropogenic pressure on threatened delphinids.

ecology↗

bioRxiv2025

Range and elevation predict responses to climate change in frogs and lizards in the Western Ghats biodiversity hotspot of peninsular India

Anthropogenic climate change is altering the environment at unprecedented rates with severe consequences for most living organisms. As a result, species may extend, truncate, or shift their ranges in order to adapt to changing conditions. Species Distribution Models (SDMs) provide a data driven approach to predict future distributions under climate change and prioritize areas for conservation. Here, using a 10-year dataset with 4049 occurrence records of frogs from eight families and 27 genera as well as 733 occurrences of lizards from two families and 11 genera across the Western Ghats, we built SDMs to assess the changes in species distributions due to climate change. As expected, the temperature gradient across elevation and seasonality gradient across latitude contribute most to the climatic limits of species distributions. Latitudinal extents of most species were narrower in future predictions compared to the present, but there was little shift in latitudinal positions. On the other hand, most species shifted their distributions towards higher elevations, but the elevational range sizes remained the same. A total of 75 species of frogs (55%) and 15 species of lizards (45%) lose more than half of the suitable area, with few exceptions in both taxa that show an increase. In cases where a shift or increase in distribution was observed, the ability of the species to access and survive in these areas remains uncertain due to discontinuous topography and the presence of sister species. Overall, the frog and lizard fauna of the Western Ghats will be severely affected by climate change in the future due to a loss in climatic suitability.

ecology↗

bioRxiv2025

Integrated deep learning and geo-referencing for drone-based animal tracking with flexible camera angles

O_LIThe ability of drones to provide detailed information on animals and their surroundings makes them ideal for studying animal behaviour at fine scales. While drones can provide high-resolution images of what animals are doing, they should also, in theory, be able to provide data on where they are. However, reconstructing geo-referenced tracks from drone videos that follow animals is challenging, particularly because current methods require specific drone flight patterns and large computational power. C_LIO_LIHere, we combine deep learning and object tracking methods with a novel geo-referencing algorithm which allows us to track individuals across video frames and reconstruct their geo-referenced trajectories. We used a Region-based Convoluted Neural Network to detect animals and a Hungarian tracking algorithm to link detections across video frames, and then geo-referenced each detection in every frame to reconstruct individual trajectories. C_LIO_LIWe tested our geo-refencing algorithm through multiple drone flights with varying flight parameters over known Ground Control Points. The median (95% CI) geo-referencing error was 2.81 (0.74 - 23.23) meters, which reduced by 50% when the drone camera was positioned between -90{degrees} and -40{degrees}. Error increased with drone height and camera angle (-90{degrees} refers to the camera pointing towards the ground) but was not impacted by drone orientation. C_LIO_LIWe then demonstrate the utility of our framework with empirical examples using consumer-level drones. First, we tracked a volunteer carrying a high-resolution GPS unit and overlayed their GPS tracks on our estimated tracks to quantify tracking error. Next, we used drone videos of two delphinid species (Tursiops truncates gephyreus, and Sousa plumbea) representing varying environmental and flight conditions. We were able to successfully infer individual tracks across all conditions except when individuals formed tight clusters, in which case tracks were assigned a group identifier. C_LIO_LIOur framework demonstrates an easy and robust approach to translate drone videos of moving animals into geo-referenced animal tracks which is applicable in many research contexts. A major advance over previous methods is that our algorithm is robust to different camera angles, and provides tracks with accuracy on-par with, or even exceeding, the accuracy from GPS tracking. C_LI HeadlineAutomated drone-based animal tracking

ecology↗

bioRxiv2024

Species rich but data poor: leveraging distribution modelling techniques to map cetacean occurrence in South Asian waters

Cetaceans play important ecosystem roles but are challenging to study since they are highly mobile and spend their entire life at sea. More than a third of all cetaceans occur in South Asian waters where they overlap with several key threats including fisheries, pollution, and high vessel traffic. However, baseline information on their occurrence at the sub-continental scale is lacking even for relatively well studied species. To address this gap, we collated sighting information on cetaceans from the North Indian Ocean region (5-25{degrees}N, 65-95{degrees}E) and used species-tuned distribution models and ensemble modelling approaches with physiographic and oceanographic predictors to map habitat suitability and species richness. We used Multivariate Environmental Similarity Surfaces (MESS) indices and expert reviews to validate our predictions and better infer species distribution. We collated 2329 sighting records for 31 species and modelled the distribution of 18 species. Areas of high species richness, defined by high slope and bathymetric complexity, occurred along the east coast of India, in south Sri Lanka, and around the Lakshadweep and Andaman and Nicobar archipelagos. Species richness patterns were generally consistent with the six identified ecoregions in the area. Most of our predictions were given high scores by the expert reviewers. Our maps underpredicted the occurrence of a few oceanic species, highlighting the need for focused offshore surveys, and overpredicted areas with high MESS indices for all species. We discuss the occurrence patterns and their drivers for these cetacean species while highlighting knowledge gaps and the importance of fine-scale distribution data for conservation planning, especially during the development of regional management plans for cetaceans.

ecology↗

bioRxiv2024

To nest or not to nest: environmental cues for olive ridley mass nesting events in Odisha, India

Sea turtles of the genus Lepidochelys take part in synchronised nesting events, known as arribadas, where a large number of females emerge simultaneously from the sea to nest on the beach. Despite some evidence for the role of environmental factors, there is considerable uncertainty about both the factors that influence mass-nesting at an annual scale as well as the onset of individual events. We used a multi-decadal dataset from two olive ridley mass nesting beaches in Odisha, India, to identify the environmental factors associated with inter-annual nesting variation, nesting seasonality and the onset of arribadas. Interestingly, the two sites showed different patterns in inter-annual patterns associated with the non-occurrence of arribadas, despite being only 250 km apart. The nesting season was consistently during the dry and cooler part of the year. Arribada start dates were non-uniformly distributed across the lunar phase in Gahirmatha with most arribadas occurring during the first and third quarters. Fast Southern Winds characterised the period before and during the arribada at both sites. Machine learning models (XGBoost) identified the most important parameters for the onset of mass nesting and accurately predicted more than 75% of the start dates. Lunar phase, mean sea level pressure and wind speed and direction were important parameters at both sites. Differences in parameter importance between sites suggest that mass nesting is influenced by the interaction of several environmental parameters, along with site-specific characteristics. Insights into the triggers of mass nesting can thus provide guidance for site-specific management efforts.

ecology↗

bioRxiv2024

Are super-predators also super-scary? A systematic review and meta-analysis of animal responses to human interactions

Humans interact with wild animals through lethal and non-lethal activities. While theory predicts that these interactions should alter animal behaviour, the relative magnitude of impact is not well understood. We conducted a systematic review and meta-analysis of the past 30 years of research, focusing on changes in foraging, vigilance, and movement behaviours in wild animals. We found that lethal human activities (e.g., hunting) cause significant behavioural changes, with targeted species increasing vigilance and reducing foraging in affected areas. Active non-lethal activities (e.g., tourism) elicited similar but weaker patterns, with many species showing little to no change in their behavioural responses. In contrast, passive non-lethal interactions (e.g., roads) produced highly variable responses. Overall, human-induced fear elicits responses in wild animals that broadly align with predictions from the risk allocation hypothesis. However, the magnitude and direction of animal responses depend on the type of human activity and the ecological context. The most pronounced behavioural changes occurred where humans posed a direct lethal threat. Gaps in the literature, uneven data within and across species, and limited information on the history or context of interactions currently limit our ability to better predict when and why animals change their behaviour in response to humans.

animal behavior and cognition↗

bioRxiv2024

Human like severe hypertriglyceridemia in a high fat fed chicken model

Cardiovascular disease (CVD) is the biggest cause of mortality globally. Controlling the risk factors for CVD such as blood cholesterol and triglycerides is the hallmark of primary prevention of CVD. There are several drugs to control cholesterol that are available but not many approaches to reducing triglycerides safely are available. High blood triglycerides or hypertriglyceridemia in humans is classified as moderate (200-400 mg/dl plasma levels) severe (400-800 mg/dl) and very severe (>800 mg/dl). There are not many appropriate in vivo models to study human like severe hypertriglyceridemia. We show here that high fat fed chickens rapidly and in a sustained manner respond by demonstrating triglyceride levels reminiscent of severe hypertriglyceridemia in humans. Such a model could be useful in better understanding this human disease as well as serve to test new therapies.

pharmacology and toxicology↗

bioRxiv2023

Ant impacts on global patterns of bird elevational diversity

Across the worlds mountains, elevation-species richness relationships are highly variable. Here, using data on bird species elevational distributions from all 46 of the worlds major mountain ranges, bird species dietary traits, and the distribution of the low-elevation ant genus Oecophylla, we show that global patterns in bird elevational diversity are likely to be affected by competition with ants. Oecophylla is an exceptionally abundant and aggressive predator of invertebrates, which preys on the same species that sympatric invertivorous bird species feed on. In mountain ranges with Oecophylla present in the foothills, maximum species richness of invertivorous birds occurs, on average, at 960m, [~]450m higher than in mountain ranges without Oecophylla. Further, in mountain ranges with Oecophylla, species richness of invertivorous birds increases initially with with elevation to produce a mid-elevation peak in invertivore bird species richness. Where Oecophylla is absent, invertivore bird species richness generally shows monotonic declines with increasing elevation. We attribute the pattern to the following mechanism: first, Oecophylla reduces prey density for invertivorous birds; second, low invertebrate prey abundance reduces invertivorous bird density and third, lower bird density is correlated with lower bird species richness. Because invertivores dominate montane bird communities, global elevational bird diversity patterns are also driven by Oecophylla. The findings emphasize how competitive interactions between distantly related taxa set geographical range limits.

ecology↗

bioRxiv2021

Connectivity networks and delineation of distinct coastal provinces along the Indian coastline using large-scale Lagrangian transport simulations

Ocean circulation defines the scale of population connectivity in marine ecosystems, and is essential for conservation planning. We performed Lagrangian transport simulations and built connectivity networks to understand the patterns of oceanographic connectivity along the Indian coastline. In these networks, nodes are coastal polygons and the edges connecting them represent the magnitude of larval transfer between them. We assessed the variation in connectivity networks within and between two monsoonal seasons, across El Nino-Southern Oscillation (ENSO) years and for pelagic larval durations (PLD) up to 50 days. We detected well-connected communities, mapped frequent connectivity breaks and ranked coastal areas by their functional role using network centrality measures. Network characteristics did not differ based on the ENSO year, but varied based on season and PLD. Large scale connectance (entire Indian coastline) was small, ranging from 0.5% to 3.4%, and the number of cohesive coastal communities decreased from 60 (PLD <4 days) to 30 (PLD >20 days) with increasing PLD. Despite intra-seasonal variation in connectivity breaks, four disconnected provinces were consistently identified across the entire PLD range, which partially overlapped with observed genetic and biogeographic breaks along the Indian coastline. Our results support the adoption of an adaptive regional management framework guided by fine-scale analysis of connectivity within the four provinces delineated in the present study. A few sites within each province displayed notably higher centrality values than other nodes of the network, but showed variation with season and PLD, and could be targeted for national and transnational conservation and management plans.

ecology↗